In a field of analytical chemistry, various apparatus and sensors for obtaining desired information such as concentrations or components of object to observe process or result of chemical and biochemical reactions are developed. The apparatus have been reduced in sizes with use of a semiconductor manufacturing method. In addition, a concept called “a micro total analysis system (μ-TAS)” or a “lab-on-a-chip” is under development, in which all processes for obtaining the desire information are performed on a micro device. In μ-TAS, a collected unrefined sample is caused to pass through the micro device to undergo a process such as sample refinement or chemical reaction, thereby obtaining concentration information of the component contained in the final sample or obtaining a further chemical compound. A refinement method or a chemical reaction control method used in the process, the development of a micro valve and a micro pump for use in a fluid control method, and a surface treatment method are also object to be studied in the field of the μ-TAS.
A capacity of a fluid being contained in the micro device is lower when comparing with conventional desktop-size analytical equipment. Therefore, when the micro device is used, as the reduction in the total amount of fluid is expected, the necessary amount of reagent for the use of the analysis and the length of the reaction time between the sample and the reagent are also expected to be reduced. An advantage of the micro device has been recognized and an attention has been focused on technologies associated with the μ-TAS in recent years. Phenomena such as an increase in interfacial surface to volume ratio and mixing of solutions due to diffusion, which are caused by a reduction in size of the device, have been widely studied. There have been many reports in which detection sensitivity is improved by the micro device as compared with a conventional type device (see Petra S. Dittrich, Kaoru Tachikawa, and Andreas Manz, “Micro Total Analysis Systems. Latest Advancements and Trends”, Analytical Chemistry, 2006, Vol. 78, No. 12, pp. 3887 to 3908).
A device using a micro channel is constructed such that a normal channel width thereof is approximately 50 μm to 200 μm. The channel width substantially corresponds to a diameter of a multimode optical fiber. When a fluid has a higher refractive index than a material serving as the micro channel, light can be propagated through the fluid by filling the micro channel. An attention is being focused on a technology called optofluidics in which a micro fluid and light are combined together as described above. The light incident on the micro channel is repeatedly totally reflected on a channel wall surface, and then propagates through the micro fluid while the light is confined to the micro fluid on the same principle as the case where light propagates through an optical fiber (see Demetri Psaltis, Stephen R. Quake, and Changhuei Yang, “Developing optofluidic technology through the fusion of microfluidics and optics”, Nature, 2006, Vol. 442, pp. 381 to 386).
A method of detecting a sample contained in a fluid filling a channel using light propagating through the fluid is disclosed, and the light is propagated through the channel made of fluorocarbon which has a lower refractive index than water, thereby detecting the sample (see Japanese Patent Application Laid-Open No. H07-218422). A method of coating an inner wall of a channel with an amorphous fluoropolymer which has a lower refractive index than water while a channel material has a higher refractive index than water, thereby confining light to the channel is also disclosed (see Japanese Patent No. 3260431).
A method using evanescent light is disclosed as a method of detecting a sample included in a channel with light at high sensitivity (see Japanese Patent Application Laid-Open No. 2006-177878). The evanescent light is generated from light propagating through an optical fiber or a waveguide. The evanescent light is light propagating while exuding to the outside of the fiber core or the waveguide, and exponentially reduces in intensity in a direction perpendicular to the propagation direction of the light. Therefore, in a case where the waveguide is formed close to the channel or to serve as an inner wall of the channel, when the evanescent light is penetrated into the channel, only a vicinity of a surface of the channel is irradiated with the light, and hence the method is suitable to detect the sample on the surface of the channel. The sample can be detected by the evanescent light at a high S/N ratio by preventing light propagating through the waveguide from being affected to the detection.
However, according to the method of detecting the sample contained in the fluid with the light propagating through the fluid using the channel made of fluorocarbon, the high-sensitivity detection is difficult because the light propagates through the entire channel, hence the S/N ratio becomes low.
Water is preferable solvent when handling a biological sample. When water is used in a channel, in order to propagate light through the channel, a device or coating material is limited to a material which has a lower refractive index than water. Examples of a material of the channel of a micro fluid device include glass, polycarbonate, cyclic polyolefin, and polydimethylsiloxane, which are frequently utilized as a micro channel material. However, each of the materials of the channel has a higher refractive index than water, and hence the detection method of propagating the light through the channel cannot be realized. Although amorphous fluoropolymer coating may be possible, some polymer material cannot be used for amorphous fluoropolymer coating. Therefore, the detection method using the amorphous fluoropolymer has a problem that there is a limit on the device material.
As to the detection method using the evanescent light generated by the waveguide located close to the channel, it is known that the detection light intensity is improved with an increase in the amount of contact between the evanescent light and the sample. In contrast to this, only the vicinity of the surface of the channel is irradiated with the evanescent light to contribute to the detection, and hence a sample which is not located close to the surface corresponds to a dead volume at the time of detection. Therefore, in order to penetrate the evanescent light into the channel and thus to detect the sample located at a position deeper than the surface of the channel, a method of adjusting one of a refractive index and a width of the waveguide can be employed. However, in the case of the conventional light detection using the waveguide, the waveguide is made of a solid material, and hence the refractive index or the width of the waveguide in the manufactured device cannot be adjusted. In other words, there is a problem that the detection sensitivity cannot be adjusted after the device is manufactured.